1. Field of the Invention
The invention relates to a process for the preparation of PDGF-A and biologically active PDGF-AA and PDGF-AB.
2. Brief Description of Related Art
Platelet derived growth factor (PDGF) is a major mitogen in serum which promotes growth of fibroblasts and smooth muscle cells in vitro. In vivo, PDGF is stored in the a granules of the platelets and released after stimulation of the platelets. Highly purified PDGF is a basic protein which displays a considerable heterogeneity with regard to its molecular weight (27,000 to 31,000 d). The reasons for this heterogeneity are aging, processing and the existence of various isoforms of type AA, AB or BB. The biological activity of all these forms is destroyed by reduction of the disulfide bridges. Human PDGF from platelets consists principally of AB heterodimers (Heldin, C.-H. & Westermark, B. (1984) Cell, 37, 9-20; Deuel, T. F., Tong, B. D. & Huang, J. S. (1985) Current Topics in Cellular Regulation, 26, 51-61; and Ross, R., Raines, E. W. & Bowen-Pope, D. F. (1986) Cell, 46, 155-169.).
Amino-acid sequencing in conjunction with DNA sequencing of the genes have shown that A and B are homologous (Betsholtz et al. Nature 320, 695-699, 1986). PDGF-B is virtually identical to the transformed gene product P.sub.28.sup.v-sis of simian sarcoma virus (SSV). Corresponding homodimers of type BB have been detected in SSV-transformed cells and showed properties similar to those of PDGF from platelets. However, these BB dimers were secreted to only a small extent from the infected cells. PDGF-AA forms are, by contrast, secreted efficiently by producing cells (Heldin et al. Nature, 319, 511-514, 1986). There is an increasing amount of evidence that the three isoforms, AA, AB and BB, assume different functions. Thus, for detailed investigations, it was necessary to develop a process for producing larger quantities of PDGF-A, PDGF-B, PDGF-AA and PDGF-AB.
Compare EP-A-0 288 307 for the use of PDGF for wound treatment.